1. Field of the Invention
This invention relates to the field of overhead projectors, and more particularly to the field of accessories for overhead projectors to facilitate the handling of transparencies to be projected.
With the advent of relatively compact, inexpensive overhead projectors, these devices have become very popular for making presentations of printed matter, sketches, charts, and the like, such as those made by salespersons or executives or made by teachers in the classroom. Thus, a plurality of transparencies containing information helpful to the presentation are prepared and then are sequentially positioned on the light table of an overhead projector during the presentation.
2. Description of the Prior Art
A problem which has plagued the sequential projection of transparencies is that of positioning the transparency on the light table of the projector. Another problem is that of continuing projection as a given transparency is being replaced. Thus, leaving the projector light on while changing transparencies has proven highly disruptive to the presentation.
It also has been a problem of facilitating positioning of transparencies and light control where there are a variety of different overhead projectors available which simply have a light table. Thus, a user is confronted with the need for a transparency device which is portable and adapted to be used with the light tables of a variety of different projectors.
Certain light projectors are provided with built-in stages for positioning transparencies and with built-in devices for blocking the projection light while a transparency is being changed; however, such stages and devices ar enot available to be used with other projectors since they are integrated or built-in to a given projector.
As to light control, the common technique is to turn on the projector light only after a transparency is positioned, and then turn off the projector light while changing the transparency. It can readily be imagined that this solution produces considerable wasted motion on the part of the individual making the presentation and generally slows down the presentation. Another technique is to use an expedient device to block the light. For example, one expedient method is to tape one edge of a piece of cardboard over the projector lens. The cardboard can be flipped down while changing transparencies, and flipped up to show slides. As with most field expedients, a technique of this nature detracts from the professionalism of a presentation, and is subject to problems such as the tape cracking or becoming fatigued in the midst of a presentation.
Techniques such as those discussed above are relatively common because solutions proposed by the art have been cumbersome or expensive. For example, U.S. Pat. No. 3,510,214 which issued on May 5, 1970 to Crow, proposes an adaptor accessory for overhead projectors which takes several embodiments, each requiring a permanent installation to the projector. The necessity for a permanent installation due to the complexity of the device, prevents the device from being portable for use with different projectors. Similarly, U.S. Pat. No. 3,661,449 which issued on May 9, 1972 to Wright also requires a permanent installation on a projector. The device of Wright includes several shutters for varying portions of a transparency to be exposed, but at the price of a relatively complicated piece of equipment which is not portable. Thus, such a device would not be suitable for a person to carry in for example, a brief case, and would not enable the person who must make presentations at a variety of locations using a variety of overhead projectors (such as a salesperson).
Each of U.S. Pat. No. 3,531,193 which issued on Sept. 29, 1970 to Diehl, U.S. Pat. No. 3,084,594 which issued on Apr. 9, 1963 to Ray, and U.S. Pat. No. 2,767,611 which issued on Oct. 23, 1956 to Gerald show projection devices in which devices for positioning a transparency and a shutter device are integrated or built into the projector. Thus, these patents do not disclose a portable presentation device as that of the invention.
Although the art may have produced devices said to be suitable for permanent installations, a need remains for a simple, portable, and easy to use device that allows a person to make effective presentations using a variety of projectors.